It is known to encapsulate perfume in small capsules (or micro-capsules), typically having a diameter less than 1000 microns, for a variety of reasons relating to the protection, delivery and release of perfume. One type of capsule, referred to as a wall or shell capsule, comprises a generally spherical hollow shell of perfume-insoluble material, typically polymer material, within which perfume is contained.
Various methods are known for making shell capsules, including in situ polycondensation for producing so-called aminoplast resin capsules from urea-formaldehyde or melamine-formaldehyde polymers. Briefly, the process involves forming a dispersion or emulsion of the perfume in an aqueous solution of urea-formaldehyde or melamine-formaldehyde precondensate under appropriate conditions of agitation to produce capsules of a desired size, and adjusting the reaction conditions to cause condensation of the precondensate by acid catalysis, resulting in the condensate separating from solution and surrounding the dispersed perfume fill to produce micro-capsules.
Perfume-containing aminoplast capsules are currently primarily used in the area of perfume sampling as so-called “scratch and sniff” products, where the capsules are applied to paper or cardboard and show excellent perfume retention properties over extended periods, with the capsule functioning to prevent evaporation of the perfume until the capsules is ruptured. Such capsules can similarly be applied to textiles etc, and also show good stability.
It has been proposed to use such capsules in shampoo and other aqueous surfactant-containing products to give various fragrance effects, e.g. burst release in-use, enhanced deposition, longevity, stability improvement etc. However, in practice serious storage problems arise with shell encapsulates in such products, in that surfactant is able to enter the capsule through the wall and causes the perfume contents to leach out. Aminoplast capsules are most resistant to this effect, but nevertheless still exhibit quite rapid perfume loss such that they are of no practical use in such products. In this connection, see the article “Use of amino resin microcapsule dispersions in cosmetics” in Parfumerie und Kosmetik, 72 Jahrgang, Nr. 7/91.
The present invention is concerned with modified aminoplast capsules having properties enabling use in aqueous surfactant-containing products.